1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for reporting Packet Data Convergence Protocol (PDCP) status in a wireless communication system.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
Minimization of driving tests (MDT) is a test performed by operators for coverage optimization by using a user equipment (UE) instead of using an automobile. A coverage varies depending on a location of a base station, deployment of buildings nearby, a user's usage environment, etc. Therefore, it is required for the operators to periodically perform the driving test, and a lot of costs and resources are consumed. The MDT is used when the operator measures the coverage by using the UE.
One of the objectives of the MDT is Quality of Service (QoS) verification. Usage of UE specific QoS measurements is to verify performance relevant to end user perception. This also allows detecting critical conditions and determining the need to change the network configuration, parameter settings or capacity extension. Operators may use this information to assess the actual QoS experienced by the end user, check whether the actual QoS meets the planning target, and find critical factors determining actual QoS. Operators may also use this information together with the location information to draw a QoS map of the cell.
For QoS verification, there is a need to measure actual user throughput. Logging of data volume for a given Data Radio Bearer can be used to derive the user throughput. The data volume can be defined in terms of number of bytes of Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) in the logging period.
To log the data volume transmitted and received by the UE, the UE has to calculate the amount of data each time it transmits or receives, and also keeps the result of calculation until it reports the result to a base station. It may increase UE complexities, and waste UE memory and battery.